Antiproliferative activity and apoptosis induction by trijuganone C isolated from the root of Salvia miltiorrhiza Bunge (Danshen)

In this study, we found that the hexane fraction of Danshen, the dried root of Salvia miltiorrhiza (Lamiaceae), exerted antiproliferative effects on human leukemia cells. Phytochemical investigation of the hexane fraction achieved the isolation of the tanshinone diterpenes: dihydrotanshinone I (1), trijuganone C (2), trijuganone B (3), cryptotanshinone (4), tanshinone IIA (5), and tanshinone I (6). Compound 2 showed significant antiproliferative activities against human leukemia cells HL-60, Jurkat, and U937. The antiproliferative activities of 2 against human cancer and normal cells indicated that 2 exhibited potent antiproliferative activities with IC50 values less than 10 μM against HL-60 and Jurkat cells as well as on the colon cancer cells DLD-1, COLO 205, and Caco-2. Compound 2 induced chromatin condensation, DNA fragmentation, activation of caspase-3, -8, and -9, and the cleavage of poly (ADP-ribose) polymerase (PARP) in HL-60 cells. Moreover, 2 activated Bid and Bax, leading to the loss of mitochondrial membrane potential, and 2 induced the cytochrome c release from mitochondria into cytosol. In contrast, Bcl-2 and Bcl-xL were unaffected by 2. These results suggest that 2 exerts antiproliferative effects via apoptosis induction mediated by mitochondrial dysfunction and caspase activation. Compound 2 may serve as a candidate of potential chemotherapeutic agent for human leukemia.